The micro needle approach shows clear advantages over competing methods of transferring fluids through skin or other biological barriers. In contrast to hypodermic needles, micro needles are relatively painless and can be self administered or administered by non-professionals. Furthermore, when using micro needles, only 10-20% of the drug is needed compared to hypodermic needles. In addition, they overcome the molecular size limitations characteristic of conventional transdermal patches.
While hollow micro needles are potentially an effective structure for transferring fluids across or into a biological barrier, the devices proposed to date suffer from a number of drawbacks that limit or prevent their functionality. Current micro needle array devices do not reliably penetrate the biological barrier, preventing or diminishing cross-barrier transfer of fluids. In the case of administering drugs through human skin, the transfer is ineffective if the micro needle does not pierce at least the stratum corneum layer. In many cases, the skin surface is elastic enough to stretch around each micro needle without being pierced.
A system according to the preamble that addresses this drawback is known from US patent application 2005/0165358.
In the known system the displacement mechanism is arranged to achieve a displacement having a non-zero component parallel to a planar surface defined by the substrate. Once the biological barrier is penetrated by the micro needles a user should manually depress a hand-operated cover so as to apply force to a piston which forces the fluid that is present in a storage region through the hollow micro needles to form fine jets there from.